1. Field of the Invention
The present invention relates to a driving apparatus for driving a lens apparatus. More particularly, the present invention relates to a driving apparatus fitted to an image pickup lens and including a rotary absolute position detector, and a lens apparatus and an image pickup apparatus including the same.
2. Description of the Related Art
A lens apparatus of a portable type represented by an electronic news gathering (ENG) lens includes a lens barrel including an operation ring for driving a zoom lens and a focus lens, and a driving apparatus for detecting the position of the operation ring and driving the operation ring. Further, with regard to a lens apparatus used at the site of filming, delicate operation thereof is required. Thus, a lens apparatus dedicated to manual operation, that is, a lens apparatus without a driving apparatus in which the operation ring is operated only manually is known. However, when zoom operation from a wide angle side to a telephoto side at a fixed speed or the like is required, it is desired to drive the operation ring using a servomechanism included in the driving apparatus. Further, other kinds of use such as fitting and removing the driving apparatus by a user oneself are also thought of, including a case where the driving apparatus is fitted to a lens apparatus without a driving apparatus to make a film at the site of filming.
By the way, conventionally, as a position detection sensor used for a driving apparatus, a potentiometer (hereinafter also referred to as POT) or an incremental encoder is used. A POT is a sensor which detects the position of a target of the control and outputs voltage corresponding to the detected position, and can detect an absolute position.
An incremental encoder is a sensor which detects a relative change in position of the target of the control. The incremental encoder can detect a relative position more accurately than a POT, but, for the purpose of detecting an absolute position, initialization processing is necessary after power on or after a reset operation. Specifically, the initialization processing is performed by obtaining an origin pulse which is output from a Z phase to be a reference in detecting the absolute position.
Output voltage of a POT generally varies from a minimum value to a maximum value in a single rotation. However, the range in which the position can be actually detected is limited to about 340° of a single rotation (360°). The remaining range of about 20° is a dead zone in which the position cannot be detected. Therefore, it is necessary to make an adjustment for establishing correspondences between the movable range of the target of the control and the range in which the POT can detect the position.
Therefore, there is a driving apparatus using a POT as the position detection sensor which, by using a slip mechanism, makes an adjustment so that the dead zone of the POT does not overlap the movable range of the operation ring which is the target of the control after the driving apparatus is fitted to a lens barrel. However, in this case, it is necessary to additionally provide the slip mechanism.
Japanese Patent Application Laid-open No. 2005-283274 discloses a technology of, in a position detecting device using an incremental encoder and an absolute position detector (such as POT), rotating the incremental encoder multiple times for the purpose of enhancing the resolution of the position detector. The multiple rotations cause the Z phase to appear multiple times. Correspondences between the position of the Z phase and the output value of the POT are established and stored. By, when the power is turned on, driving the target to be driven to the nearest Z phase position with the output value of the POT being the clue, the absolute position can be detected.
In Japanese Patent Application Laid-Open No. 2009-276128, a position detecting device using an incremental encoder and a POT divides in advance a driving range based on the output value of the POT in a lens driving area, and an adjustment is made in advance so that only one Z phase of the incremental encoder exists in each divided area. By storing, at the time of initialization, an encoder pulse from one end point to each origin signal (Z phase) and the total pulses in the whole area, the absolute position can be determined after the power is turned on based on area detection by the origin pulse and the output value of the POT and on the number of encoder pulses which is stored.
However, the related-art technology disclosed in Japanese Patent Application Laid-open No. 2005-283274 described above is on the assumption that the dead zone of the output value of the POT does not exist in the lens driving area. Further, the related-art technology disclosed in Japanese Patent Application Laid-Open No. 2009-276128 makes an adjustment in advance so that only one Z phase of the incremental encoder exists in each area divided based on the output value of the POT. To make the above-mentioned adjustment so that the position detection sensor is located at a desired position when a lens barrel and a driving apparatus are connected to each other is very complicated and troublesome to accomplish for an ordinary user.